Factors influencing surgical residual deviation and their impact on higher-order aberrations after SMILE surgery

PURPOSE: To investigate the factors influencing the surgical residual deviation after Small Incision Lenticule Extraction (SMILE) and its impact on postoperative higher-order aberrations (HOAs). METHODS: This retrospective study included 77 patients (146 eyes) who underwent SMILE surgery at our Eye and Vision Center from February 2021 to June 2022. Surgical data collected included uncorrected distance visual acuity (UDVA), refraction, spherical equivalent (SE), corneal curvature, central corneal thickness (CCT), axial length (AL), intraoperative actual refractive correction, posterior corneal surface height (PME), total corneal HOAs, spherical aberration (SA), coma aberration (CA), and trefoil aberration. Changes in central corneal thickness were observed preoperatively and at 1 and 3 months postoperatively. The actual lenticular thickness removed during surgery was compared with the predicted lenticular thickness, and statistical analysis was performed using SPSS version 26.0. RESULTS: The average deviation of CCT at 1 month postoperative was - 7.11±9.933 µm, and at 3 months postoperative was - 13.37±9.665 µm. The difference between actual and predicted lenticular thickness showed statistical significance (P<0.05). At 1 month and 3 months postoperative, the ratio of eyes with negative deviation to positive deviation was 113:33 and 137:9, respectively. Statistically significant differences were observed in preoperative CCT, with the negative deviation group positively correlating with preoperative refraction, SE, intraoperative actual refractive correction, curvature, CCT, and PME (P<0.05). Conversely, the positive deviation group showed a negative correlation with preoperative curvature, CCT, and PME (P<0.05). At 1 month and 3 months postoperative, HOAs, SA, CA, and trefoil aberration increased compared to preoperative values, with UDVA, SE, HOAs, SA, and CA showing statistically significant differences (P<0.05). In the negative deviation group at 1 month postoperative, deviation values positively correlated with SE (P<0.05). In the negative deviation group at 3 months postoperative, deviation values were positively correlated with HOAs, SA, and CA (P<0.05). No significant correlation was found between deviation values and UDVA, SE, HOAs, SA, CA, or trefoil aberration in the positive deviation group at both 1 and 3 months postoperative. CONCLUSION: There is a difference between the actual lenticular thickness removed during SMILE and the predicted lenticular thickness. Central corneal thickness gradually increases over time postoperatively. The cutting deviation after SMILE is correlated with preoperative refraction, curvature, and PME, and has a certain impact on postoperative HOAs.